Insulation exhibiting low flame spread and smoke development is desirable for a wide variety of applications. Such applications include insulation for enclosed ducts (e.g., duct liner insulation and duct wrap insulation) and for other enclosed spaces such as public transportation vehicles, plenums in public buildings, motor and electronic enclosures, and aircraft, for example. In many of these applications, the insulation should exhibit a flame spread index of 25 or less and a smoke developed index of 50 or less as measured in accordance with the American Society for Testing and Materials E84 Test entitled “Standard Test Method for Surface Burning Characteristics of Building Materials” (hereinafter referred to as “ASTM E84”).
Inorganic fibers such as fiberglass and specially treated foams have been used in such applications. However, fiberglass can break loose in air streams such as ducts and can cause irritation. Specially treated foams tend to be expensive and have reduced acoustic performance. Foams may also have a relatively high smoke toxicity under burning conditions.
Other types of insulation used in these applications are made from materials other than synthetic fibers, such as mineral wool, polyisocyanurate foam, polyimide foam, elastomeric foams and fiberglass. However, disadvantages associated with these insulations may include high cost, relatively poor acoustic performance and/or tendency break loose and cause irritation.
Other natural and synthetic fibers, including para-aramids, meta-aramids and wool fibers, may be used in insulations for resistance to burning. However, as compared to PET fibers, for example, these fibers are larger denier and therefore less desirable for thermal insulators which achieve their maximum thermal resistance with small diameters. Furthermore, blends of para-aramid, meta-aramid and wool fibers with finer diameter PET fibers do not necessarily show low flame spread and low smoke development (i.e., in accordance with ASTM E84).
Insulation materials using synthetic fiber materials have been proposed. For example, U.S. Pat. No. 6,797,653 to Fay proposes a sprayed-on polymer surface against the thermal insulator. The Fay patent does not document weight, thickness, thermal conductivity or surface burning properties per ASTM E84. U.S. Patent Application Publication No. 2009/0133347 to Wadsworth proposes a polymer film against the thermal insulator. The Wadsworth application also does not document various properties such as range of weight, thickness, thermal conductivity and surface burning characteristics.